The present invention relates to a tantalum sputtering target having a random crystalline orientation, high deposition speed, superior film evenness (uniformity), reduced generation of arcings or particles and favorable target use efficiency.
In recent years, the sputtering method for forming a film from materials such as metal or ceramics has been used in numerous fields such as electronics, corrosion resistant materials and ornaments, catalysts, as well as in the manufacture of cutting/grinding materials and abrasion resistant materials.
Although the sputtering method itself is a well-known method in the foregoing fields, recently, particularly in the electronics field, a tantalum sputtering target suitable for forming films of complex shapes and forming circuits is in demand.
Generally, this tantalum target is manufactured by forging and annealing (heat treatment) an ingot or billet formed by performing electron beam melting and casting to a tantalum material, and thereafter performing rolling and finish processing (mechanical processing, polishing, etc.) thereto.
In this kind of manufacturing procedure, the tantalum sputtering target is manufactured in such a way that the cast structure of the ingot or billet will destroy by the hot forging, disperse or eliminate the pores and segregations, and, by further annealing this, recrystallization will occur, and the precision and strength of the structure can be improved.
Generally speaking, a molten and cast ingot or billet has a crystal grain diameter of 50 mm or more. And, as a result of subjecting this ingot or billet to hot forging and recrystallization annealing, the cast structure will be destroyed, and a generally uniform and fine (100 μm or less) crystal grains can be obtained.
Meanwhile, when sputtering is performed with a target manufactured as described above, it is said that the recrystallization structure of the target will become more fine and uniform, and uniform deposition will become possible with targets having a crystal orientation arranged in a specific direction, and a film with reduced generation of arcings and particles, and having stable properties can be obtained.
Thus, in the manufacturing process of the target, measures for making the recrystallization structure fine and uniform, and arranging the crystal orientation in a specific direction are being adopted (e.g., refer to Patent Documents 1 and 2).
When observing the mechanism of recrystallization, generally speaking, a recrystallized structure is an aggregate of individual crystals with respectively different plane orientations, and each crystal is divided by a grain boundary. Before rearrangement occurs, the strain added to the object via plastic working such as cold rolling is absorbed in the primary crystals by the transgranular slip in a certain direction, and the strain is accumulated therein.
Such strained primary crystals take on a network cell structure that is extremely fine with slightly different orientations aggregated with lattice defects such as transition, and are also separated into a plurality of different areas with significantly differing orientations. When this kind of deformation structure is heated, the cells change into subgrains (recovery process) through the combination of transition or rearrangement. The change from a cell into a subgrain hardly involves any change in the measurement.
And, it is considered that these subgrains are combined, and a specific subgrain grows to become a recrystallized core, corrodes the non-recrystallized portion, grows and promotes the recrystallization.
With a tantalum target, it is said that a target having a fully recrystallized structure based on full annealing, and, as described above, having a specific crystal orientation is favorable in stabilizing the structure.
When sputtering is performed with a tantalum target as described above, there are problems in that the evenness (uniformity) of the film will become inferior, the generation of arcings and particles will be promoted, and the quality of sputtering deposition will deteriorate.
[Patent Document 1] PCT(WO)2002-518593
[Patent Document 2] U.S. Pat. No. 6,331,233